To ensure the safe and efficient movement of traffic through a highway network during nighttime conditions, traffic signs are either illuminated or made retroreflective. The Virginia Department of Transportation (VDOT) requires that retroreflective sheeting used on construction and maintenance activity signs be a fluorescent prismatic lens type capable of being retroreflective at entrance angles as great as 50 deg with observation angles of 0.2 and 0.5 deg. Because the validity of the 50-deg entrance angle requirement was questioned, this research was conducted to determine if VDOT's specification is appropriate. Since this project was concerned with fluorescent orange construction and maintenance signs, 232 work zones in Virginia for the 1999 construction season were identified and inventoried. From these sites, 1,865 signs were investigated. The information collected included position, offset, height, shape and dimensions, whether tilted forward or back, rotation and twist, and the number of approach lanes facing the sign. This information was compiled in a spreadsheet, and a vector-based model was developed to determine the entrance, observation, rotation, and orientation angles for each sign. The results indicated that VDOT's 50-deg entrance angle requirement is not appropriate for fluorescent orange construction and maintenance signs. However, the results also indicated that more emphasis should be placed on observation angle requirements than on entrance angle requirements. Every motorist on the approach to a sign will have an observation angle of 0.2, 0.5, 1.0, 1.5, and possibly 2.0 deg depending on the type of vehicle being driven. The study recommends that VDOT specify a 40-deg entrance angle and a 1.0-deg observation angle for prismatic fluorescent orange work zone signs. In addition, the study recommends that the specification include requirements for orientation and rotation angles.
Abstract